The present invention relates to a magnetron atomization source having a target body with a mirror-symmetrical, concavely constructed atomization surface with respect to at least one plane, a magnetic circuit arrangement operable to generate a magnetic field over the atomization surface, including an anode arrangement, a receiving frame which extends around an edge of the target body and is electrically insulated with respect thereto, which receiving frame has a receiving opening for at least one workpiece to be coated, and on the side of the source, a process space bounded essentially by the atomization surface of the target body and a surrounding non-atomized residual interior surface of the receiving frame. Moreover, the present invention relates to a method of use thereof in which storage disks, such as CDs, are provided with an atomization coating.
Magnetron atomization sources are generally described in DE-OS-24 31 832; EP-A-0 330 445; EP-A-0 311 697; U.S. Pat. No. 5,164,063; and DE-PS-40 18 914.
DE-PS-35 06 227 describes an improved magnetron atomization source which has one or two target bodies forming a centrically mirror-symmetrically concavely constructed atomization surface. A workpiece which, in top view, has a significantly smaller diameter than the diameter of the cup-shaped target body is inserted by way of a holding device for the purpose of atomization coating. Magnetic circuits, which are an arrangement of active elements such as permanent magnets and/or electromagnets, as well as of passive elements such as ferromagnetic elements, for example, of iron yoke parts and air gaps are provided to generate a magnetic field of the type basically known in the case of magnetrons. The magnetic circuits operate separately for the bottom area of the atomization surface and its arched edge area, respectively.
DE-A-28 24 289 describes the atomization surface of a target body on a magnetron atomization source in a centrically concave manner and an earth shielding frame in the edge area of the target body. With respect to the target body, the anode is arranged centrically and is cooled by a medium. In this source, a workpiece to be coated is generally arranged above the illustrated source. That is, the workpiece is arranged above the earth shielding frame which surrounds the edge of the target body.
EP-A-0 393 957 discloses a magnetron atomization source which has a centrically concavely shaped-in atomization surface of the target body. A workpiece to be atomization-coated is arranged far away from the source.
In many cases and specifically also in the case of the use of the magnetron atomization surface preferred according to the present invention for the coating of storage disks, for example, of optical storage disks (such as magneto-optical disks), video disks or audio disks (such as compact disks), short coating times with long service lives of the used target bodies must be achieved. This requirement has the effect, among other things, that as a high proportion as possible of the material atomized from the atomization source is deposited as a coating material on the workpiece surface to be coated.
Known atomization sources of the type mentioned above have a disadvantage, however, that, because of, among other things, the large surfaces which are neither an atomization surface of the atomization source nor a surface of a workpiece to be usefully coated, a relatively high percentage of the material atomized from the atomization surface of the target is uselessly deposited on other surfaces defining the process space. This useless deposition drastically reduces the above-mentioned yield, and significantly reduces the coating speed as well as the service life of a target body. As a result, per target body fewer workpieces can be coated with the given layer thickness.
In addition, more cleaning intervals are required in order to ensure operational reliability, and higher operating power is required to implement desired rates. In turn, thermal stress to the source and to the workpieces is increased. All of the foregoing has a negative effect on the efficiency of a production system.
The above-mentioned disadvantages also apply to the magnetron atomization source described in DE-A-42 02 349 which has a centrically concavely constructed target body, a magnetic circuit arrangement which generates a magnetic field above the atomization surface, an anode arrangement, and a receiving frame which surrounds the edge of the target body and is electrically insulated with respect to it and has a receiving opening for a workpiece disk to be coated. In this known source, the process space is defined essentially by the atomization surface of the target body and the interior surface of the receiving frame. During operation, the process space is closed off by the workpiece disk placed on the receiving opening of the receiving frame.
Considering the fact that the conventional receiving frame, as an example of a surrounding non-atomized residual interior surface, extends on the outside around the edge of the target body, the length of the cut of the interior frame surface already visible in the cross-section results in a large ring surface which is neither usefully atomized nor usefully coated. It is not significantly smaller than the new atomization surface of the target body but larger than the surface of the receiving opening. Thus, although a high percentage of the walls bounding the interior surface of the process space are coated, they are not usefully coated, thereby still causing lower efficiency.
It is an object of the present invention to eliminate the above-mentioned disadvantages and to improve efficiency. This object has been achieved in a magnetron atomization source in accordance with the present invention by providing that the process space, apart from the receiving opening for the at least one workpiece, is bounded essentially by the atomization surface, and reducing the surrounding non-atomized residual interior surface to a respective minimum which, during atomization operation, ensures a stable plasma discharge.
As a result of the fact that, according to the present invention, the atomization surface of the target body essentially defines the process space, apart from the workpiece placed during the operation, a significant improvement of the ratio between the atomized-off material quantity and the material quantity deposited as a layer on the workpiece or the workpieces is achieved and results in a significant efficiency increase.
Preferred surface ratios are obtained according to the present invention by providing that the relationship of the residual interior surface, such as that of the receiving ring, and that of the atomization surface of the target body are such the former is less than or equal to 50% of the latter.